P22,
Vmcg is figured for nil wind (US) and 7kt (UK) - not sure what JAA opts for. This leads to the occasional silly difference between the RTOW data for one operator compared to another where the minV1 in the UK AFM is higher than the corresponding US AFM.
On what basis do you state that Vmca generally is less than Vmcg ?
Mutt,
The US document is AC 25-7A at whatever issue is current - I am relying on memory for the number as I am away at the moment. My file copy is superseded and I have yet to get around to updating it - the AC at the issue I have requires that Vmcg be predicated on nil wind and I would be surprised if that has changed.
I have seen the 7 kt reference in a number of BCAR AFMs and, as I recall, we did chase up a source document about 20 years ago when we were playing with a lovely old queen of British technological prowess armed with lots of wind-walloping engines - actually we were playing with a number of them. I don't suspect that the document is still on our files and can't for the life of me remember the detail. Suggest you direct the question to Genghis - he should be able to help without too much effort - after all, he is in the right sort of place to dig it out of the archives.
Bellerophon offers a 747 Vmcg correction figure of 1.3kt/kt crosswind - quite alarming - I had always worked on a rough figure of 0.5kt/kt (for twins) based on manufacturer's data provided for a specific flight test program.
Either way, if a takeoff be predicated on minV1, the altitude/OAT be thrusty, and the cg be aft, then a strong crosswind could well see the pilot losing control above V1 in the event of an engine failure on the windward side - as the wind provides an additive destabilising yawing moment not considered in the certification process.
As to whether this situation is likely to occur or not is not the point at all. The pilot ought to be aware of the problem so that a suitable operational decision appropriate to the day can be made as and when the situation calls. Captain Airclues makes some very relevant observations regarding base training.
Contemplating where pilot handling is most demanding for a failure, I suggest not at V1 or 200ft, but rather during the rotation flare just as the pilot loses the visual horizon reference. At this point the manipulative workload and I/F scan requirement is most demanding and the potential flight path gyrations the most interesting - especially if bank is ill-controlled with a subsequent Vmca departure. I train progressively to competence at conditions of minV2/min AUW, aft CG, SL STD conditions with a bird strike if the sim has that option. When the guys can handle that comfortably, their confidence is maximised and anything else is no sweat. One also must train at the high weight, high altitude, high deviation end of the spectrum to cover the situation which is most demanding from the viewpoint of milking every drop of performance from the aircraft following a failure.
And we all take great pains not to go outside the obstacle splays ..... don't we ?
[ 16 November 2001: Message edited by: john_tullamarine ]